Low-loss printed circuit board antenna structure and method of manufacture thereof

ABSTRACT

The present invention provides a method of manufacturing an antenna structure. In one embodiment, the method includes forming an antenna trace on a substrate proximate a ground plane of the substrate. In addition, the method includes creating an insulation region extending through the substrate and located between the antenna trace and the ground plane.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

This application is a continuation of U.S. Ser. No. 10/126,600, filedApr. 19, 2002, now U.S. Pat. No. 6,759,984, which claims the benefit ofU.S. Provisional Application No. 60/295,191 entitled “LOW-LOSS PRINTEDCIRCUIT ANTENNA,” to Jan Wielsma, filed on Jun. 1, 2001, which iscommonly assigned with the present invention and incorporated herein byreference as if reproduced herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, communication devicesand, more specifically, to an antenna structure having a low-loss andhigh efficiency, and a method of manufacture thereof.

BACKGROUND OF THE INVENTION

Printed circuit boards (PCBs) are the benchmark for mounting electroniccircuit components in today's communications hardware. Conventional PCBsinclude a rigid substrate to provide support for mounting electroniccomponents in communications devices. In addition, conductive materialsare plated over such substrates and etched to provide electricallyconductive traces for interconnecting these components. For manycommunication devices, an area or a whole layer of such a PCB is oftenreserved as a ground plane serving as a reference ground for mountedelectronic circuitry. Therefore, PCBs may be manufactured with multiplelayers, each interconnected with conductive vias, to further provideelectrical connections for complex electronic circuitry.

For many communications devices, antennas are typically formed on thesame PCBs, which also carry transmitting and receiving radio frequency(RF) circuitry. A common technique employed to form antennas on PCBs isto simply etch an antenna trace, similar to the traces mentioned above,having an antenna feeder trace coupled to desired components on the PCB.Since space is limited in the ever-decreasing size of today'scommunications devices, such antenna traces are typically formed nearone or more ground planes formed on the same PCB. In such arrangements,a portion of the PCB substrate, typically the area of a PCB having thehighest density of electromagnetic energy, remains in between theantenna and the ground plane, leading to antenna efficiency degradation.

More specifically, as radio signals travel along an antenna trace, aportion of the signals are typically “lost” through energy loss ordissipation in the medium around the antenna trace, especially themedium between the antenna trace and the ground plane. The portion oftotal initial RF signals radiated into the surrounding space determinesthe antenna transmission efficiency (measured in dB) of the antenna. Thesame principle applies for antenna reception. Ideally, a 100% (0.0 dB)efficiency would be achieved if all of the RF signals traveling throughthe antenna were radiated into the surrounding space. However, as may beexpected, the material from which a PCB is constructed has a largeimpact on the percentage of RF signals that are dissipated into PCBmaterial surrounding the antenna structure. So-called “lossy” PCBs, suchas the popular FR-4 PCB, are composed of materials (e.g., fiberglass andepoxy) that dissipate a relatively large amount of the signal. However,because lossy PCBs are both inexpensive to manufacture and process,manufacturers are eager to utilize them in an effort to drive downoverall manufacturing costs. On the other hand, since RF signal lossbecomes more important as transmission frequencies increase, the currenttrend in communications devices from 2.4 Ghz to 5 GHz technology mayseverely limit all future use of less expensive lossy PCBs.

Faced with the problem of RF signal dissipation, some manufacturers havechosen to employ low-loss PCBs, manufactured from materials that allowrelatively low signal dissipation, in their communications devices.Low-loss substrates such as these usually have a dielectric losscoefficient (tg(d)) of about 0.01 or less. Examples of such substratesare the Rogers 4000 series, the PTFE, and the GTEK, each composed ofspecial mixtures of materials such as fiberglass, epoxy, Teflon,ceramic, etc. Conventional antenna structures having an antenna traceformed on low-loss substrates usually have an antenna efficiency ofabout −0.5 dB or better, which translates into a radiation efficiency ofabout 90% or more. The same antenna structure on a lossy PCB, such asFR-4, usually has an antenna efficiency of about −2.0 dB, whichtranslates into a radiation efficiency of about 65%. However, althoughproviding increased antenna efficiency, low-loss PCBs tend to drive upoverall product costs.

Another approach to reducing signal dissipation, and thus increasingantenna efficiency, has been to mount antennas above the substrate ofthe PCB. Those who are skilled in the art understand that air (e.g., anopen space) between the antenna and the ground plane provides an optimummedium for antenna efficiency. The presence of almost any material inits place leads to decrease in antenna efficiency. Unfortunately,manufacturing such 3-dimensional antennas on PCBs, even low cost lossyPCBs, typically requires at least some human intervention during themanufacturing process. Of course, human intervention into themanufacturing process typically drives up the overall manufacturingcosts of communications devices. In addition, human error that may occurduring manufacturing detracts from overall product quality andlongevity. Materials beyond the etched plated conductors used forantenna traces may further increase overall costs. Moreover, since suchraised antennas are typically held on the substrate by a limited numberof points, usually only two, the chance for antenna breakage duringproduct use is increased.

Accordingly, what is needed in the art is an antenna structure, for usewith a PCB, that does not suffer the RF signal dissipation experiencedon prior art PCBs.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides an antenna structure. In one embodiment, theantenna structure includes an antenna trace formed on a substrateproximate a ground plane of the substrate. The antenna structure furtherincludes an insulation region extending through the substrate andlocated between the antenna trace and the ground plane.

In another embodiment, the present invention provides a method ofmanufacturing an antenna structure. In one embodiment, the methodincludes forming an antenna trace on a substrate proximate a groundplane of the substrate. In addition, the method includes creating aninsulation region extending through the substrate and located betweenthe antenna trace and the ground plane.

In yet another embodiment, the present invention provides a printedcircuit board (PCB). In one embodiment, the PCB includes a substratehaving a ground plane and conductive traces formed thereon. In addition,the PCB includes an antenna structure having an antenna trace formed onthe substrate proximate the ground plane. The antenna structure alsoincludes an insulation region extending through the substrate andlocated between the antenna trace and the ground plane.

The foregoing has outlined preferred and alternative features of thepresent invention so that those skilled in the art may better understandthe detailed description of the invention that follows. Additionalfeatures of the invention will be described hereinafter that form thesubject of the claims of the invention. Those skilled in the art shouldappreciate that they can readily use the disclosed conception andspecific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following detailed description taken in conjunction withthe accompanying FIGUREs. It is emphasized that various features may notbe drawn to scale. In fact, the dimensions of various features may bearbitrarily increased or reduced for clarity of discussion. In addition,it is emphasized that some circuit components may not be illustrated forclarity of discussion. Reference is now made to the followingdescriptions taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates one embodiment of a printed circuit board (PCB)having an antenna structure constructed according to the principles ofthe present invention; and

FIG. 2 illustrates a section side view of a portion of the PCB andantenna structure illustrated in FIG. 1.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is one embodiment of aprinted circuit board (PCB) 100 having an antenna structure constructedaccording to the principles of the present invention. The PCB 100includes a substrate 110. In accordance with conventional practice, thesubstrate 110 may be a lossy circuit board, for example, the popular andinexpensive FR-4 board, which has a loss coefficient, tg(d) of about0.02 and higher, depending on the frequency. By employing a relativelyhigh loss board, such as an FR-4 PCB, the overall manufacturing costs ofthe PCB 100 incorporating the present invention may be kept low. Ofcourse, the present invention may be also employed with a low loss PCBwithout detracting from the benefits described herein.

Mounted on the substrate 110 is a ground plane 120. As is well known,the ground plane 120 provides an electrical ground connections forelectrical circuitry 130 located on the substrate 110 and mounted overthe ground plane 120. If the PCB 100 includes multiple layers, as istypically the case, the ground plane 120 may occupy several levels ofthe PCB 100, with vias interconnecting the several layers. In addition,the circuitry 130 may include vias and conductive traces (notillustrated) to electrically interconnect various components of thecircuitry 130 to each other and to the ground plane 120. In an exemplaryembodiment, the conductive traces and ground plane 120 are plated copperand are formed on the substrate 110 by etching away unwanted portions ofcopper plating. Of course, other conductive materials may be used toform conductive traces. In addition, other processes for forming theconductive traces over the substrate 110 may also be employed.

The PCB 100 further includes an antenna feeding line 140. Asillustrated, the antenna feeding line 140 is electrically coupled to thecircuitry 130 located on the substrate 110. In accordance withconventional practice, the antenna feeding line 140 provides aninterconnection between circuitry employing radio frequency (RF) inputand output signals and an antenna structure 150. In the illustratedembodiment, the antenna structure 150 includes an antenna trace 160.Both the antenna feeding line 140 and the antenna trace 160 may beformed on the substrate 110 in a manner similar to that used to formconductive traces, however the present invention is not so limited. Inaddition, the antenna feeding line 140 and the antenna trace 160 may beformed from copper, primarily because of its conductive properties, butthe present invention is broad enough to encompass other materialshaving similar characteristics.

As is commonly found on conventional circuit boards employing RFcommunications, the antenna trace 160 is formed on the substrate 110 inrelatively close proximity to the ground plane 120. As is known, thematerial comprising the substrate 110 may allow a portion of the RFsignals passing through the antenna trace 160 to dissipate in thesubstrate 110 material, which is the RF signal loss. Circuit boardscomposed of materials that lose a relatively high portion of RF signals,for example, about 35% of signals, through dissipation in the substrate110 are known as high loss or “lossy” PCBs. Such lossy PCBs are commonlyconstructed from a mixture of fiberglass and epoxy, or similarinexpensive materials, with the above-mentioned FR-4 board being onesuch example. Such lossy PCBs typically have a tg(d) of about 0.02 orhigher, and thus an antenna efficiency of about −2.0 dB or worse.

In contrast, if the material comprising a PCB only allows a relativelylow dissipation of RF signals to the ground plane 120, for example, lessthan about 15% of signals, then it is usually known as a low-loss PCB.Such low-loss PCBs are commonly constructed from ceramic, Teflon or evenspecial mixtures of fiberglass and epoxy, and typically have a tg(d) ofabout 0.01 or lower, and thus an antenna efficiency of about −0.5 dB orbetter. As discussed above, since low-loss PCBs are significantly morecostly than lossy PCBs, manufacturers have typically settled for adecreased antenna efficiency in exchange for lower overall manufacturingcosts. However, a PCB antenna structure according the principlesdisclosed herein allows the use of a less expensive lossy board, withoutsuffering from the low antenna efficiency traditionally associated withlossy PCBs.

To the accomplish this, the antenna structure 150 of the presentinvention includes an insulation region 170 formed between the groundplane 120 and the antenna trace 160. In the illustrated embodiment, theinsulation region 170 is shown as a plurality of openings (some of whichare designated 180) formed through the substrate 110 and, thus, imposingair as an insulator. However, it must be understood that the presentinvention is not limited to a plurality of openings 180, and is broadenough to encompass other types of insulation barriers. Otherembodiments of the antenna structure 150 may include a solid insulatingmaterial inserted between the ground plane 120 and the antenna trace 160to form the insulation region 170. In such an embodiment, conventionalforms of plastic (for example, ABS plastic) may be used as a solidinsulating material to create the insulation region 170 of the antennastructure 150. Other embodiments may employ conventional low-lossmaterials, such as Teflon or ceramic, as an insulating material in theinsulating region.

In the illustrated embodiment, when the insulation region 170 is formedwith openings 180, all or a substantial portion of the substrate 110originally located between the ground plane 120 and the antenna trace160 is removed. Since all or a substantial portion of the substrate 110from this location is removed (or replaced if an insulating material isused), there remains far less material of the lossy substrate 110through which RF signals may dissipate through to the ground plane 120.Therefore, the decrease in RF signal loss results in an increasedantenna transmission and reception efficiency. In those embodimentswhere an insulating material is used to create the insulation region170, the RF dissipation properties of the material would determine theantenna efficiency.

In another embodiment, the insulation region 170 is created by a singleopening 180 formed between the ground plane 120 and the antenna trace160, removing all of the substrate 110 material from that location. Insuch an embodiment, a portion of material may be left at opposing endsof the antenna trace 160 to provide at least minimal structural supportfor the portion of the substrate 110 on which the antenna trace 160 isformed. Additionally, the opening 180 may be made as large as the areaof the substrate 110 between the antenna trace 160 and the ground plane120, and extend to the edges of each. By creating the opening 180 aslarge as possible, less amount of substrate 110 material remains in thearea of high concentration of RF energy, thus avoiding the dissipationof RF signals into the substrate 110.

In an advantageous embodiment, multiple openings 180 form the insulationregion 170 by drilling holes through the substrate 110. In thisembodiment, illustrated in FIG. 1, “bridges” (some of which aredesignated 190) are left between the ground plane 120 and the antennatrace 160. As a result, a substantial portion of the substrate 110material between the ground plane 120 and the antenna trace 160 isremoved, preventing a significant amount of RF signal dissipation in thesubstrate 110. Advantageously, however, structural support is stillprovided by the bridges 190. More specifically, by leaving bridges 190between the ground plane 120 and the antenna trace 160 a strongstructure remains between the portion of the substrate 110 on which theantenna trace 160 is formed and the remaining portions of the substrate110 on which the ground plane 120 is formed. As before, the multipleopenings 180 may also be made as large as the area between the antennatrace 160 and the groung plane 120, extending the length of each, takinginto account the desired size of the bridges 190.

Turning now to FIG. 2, illustrated is a section side view of a portionof the PCB 100 illustrated in FIG. 1. As illustrated, the PCB 100 stillincludes the substrate 110 and the insulation region 170 created by theplurality of openings 180 formed therethrough. In addition, first andsecond antenna traces 160 a, 160 b are shown formed on opposing faces ofthe PCB 100. Advantageously, the multiple antenna traces 160 a, 160 bmay be employed where electrical circuitry is mounted on both faces ofthe PCB 100. Also, multiple antenna traces 160 a, 160 b may be employedto advantage where the PCB 100 includes multiple layers, having numerouselectrically interconnections therethrough.

Connecting the antenna traces 160 a, 160 b are a plurality of vias 210.The vias 210 may be formed between the first and second antenna traces160 a, 160 b to electrically interconnect them. In an exemplaryembodiment, the vias 210 are formed from the same material as theantenna traces 160 a, 160 b, however other conductive materials may alsobe employed. Although not necessary to practice the present invention,multiple antenna traces 160 a, 160 b interconnected with conductive vias210 provide further enhancement of RF signal transmission and reception,as those who are skilled in the art will understand.

By providing a PCB that includes openings between an antenna trace and aground plane, thus removing a substantial portion of the materialbetween the two, the present invention provides several benefits overthe prior art. For instance, the present invention provides forincreased antenna efficiency. As discussed in detail above, a lossysubstrate (for example, an FR-4 PCB) typically has an antenna efficiencyof about −2.0 dB, which translates into about 65% radiation efficiency.Forming openings between the antenna trace and the ground plate, thussubstantially removing the substrate material therebetween in accordanceto the principles disclosed herein, can increase antenna radiationefficiency to about 90%, with an antenna efficiency approaching about−0.5 dB or better. Those skilled in the art will understand the dramaticincrease in antenna efficiency when employing the principles of thepresent invention, even when using a lossy substrate. Furthermore, thoseskilled in the art will understand the further increases in antennaefficiency that may be achieved by incorporating the present inventioninto a low-loss substrate.

In addition, the present invention provides benefits over conventionalair antennas mounted over a substrate. For instance, conventional airantennas typically require some human intervention during themanufacturing process in order to properly mount the antennas above thesubstrate. Since an antenna trace according to the present invention isstill simply etched on the substrate, preferably along with otherconductive traces and which is typically an automated process,manufacturing costs may be substantially reduced while obtaining asignificant increase in antenna efficiency. Moreover, since the presentinvention provides for an antenna trace etched on the substrate, thefragile structure, often present with air antennas that are suspendedabove a substrate from only a minimal number of points, is eliminated.

Forming openings as the insulation region in an antenna structureaccording to the present invention is also relatively simple toincorporate into conventional circuit board manufacturing processes.More specifically, PCBs typically have numerous apertures formed thereinearly in their manufacture. These apertures may later be used formounting the PCB within a larger assembly, for receiving bond pads ofintegrated circuit chips, or even for holding the PCB in certainpositions during latter stages of manufacture. In any event,incorporating the formation of a few more openings early in the PCBmanufacturing process would be extremely simple. As a result,constructing a PCB incorporating the present invention would haveminimal, if any, impact on the time or cost of manufacturing a PCB.Furthermore, this minimal impact to the manufacturing process is thesame whether a single opening is formed between the antenna trace andthe ground plane, or whether a plurality of openings (leaving supportbridges between the two) are formed in the substrate.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. An antenna structure, comprising: a substrate having a footprint; anantenna trace having a perimeter formed on a face of said substrateproximate a ground plane of said substrate and said perimeter beingsubstantially co-planar with said face, wherein said substrate has apredetermined radio frequency loss associated therewith; and a low-lossregion extending through said substrate, wherein said low-loss region isan opening located within said footprint that extends transverse to andintersects a plane of said face, and said low-loss region locatedbetween said antenna trace and said ground plane, wherein said low-lossregion has a radio frequency loss less than said radio frequency lossassociated with said substrate, and wherein said low-loss region islocated outside of said perimeter of said antenna trace.
 2. The antennastructure recited in claim 1 further including a plurality of saidlow-loss regions.
 3. The antenna structure recited in claim 2 whereineach of said low-loss regions is separated by a portion of saidsubstrate.
 4. The antenna structure recited in claim 1 wherein saidlow-loss region is selected from a group consisting of: ABS plastic;air; ceramic; and Teflon.
 5. The antenna structure recited in claim 1wherein said antenna trace includes antenna traces located on opposingsurfaces of said substrate and connected by a via.
 6. The antennastructure recited in claim 1 wherein said substrate is comprised of ahigh loss material.
 7. A method of manufacturing an antenna structure,comprising: forming an antenna trace having a perimeter formed on a faceof a substrate having a footprint proximate a ground plane of saidsubstrate and said perimeter being substantially co-planar with saidface, wherein said substrate has a predetermined radio frequency lossassociated therewith; and creating a low-loss region extending throughsaid substrate and located between said antenna trace and said groundplane, wherein said low-loss region is an opening located within saidfootprint that extends transverse to and intersects a plane of saidface, and wherein said low-loss region has a radio frequency loss lessthan said radio frequency loss associated with said substrate, andwherein said low-loss region is located outside said perimeter of saidantenna trace.
 8. The method recited in claim 7 wherein said creatingincludes creating a plurality of low-loss regions.
 9. The method recitedin claim 7 wherein said creating includes creating a plurality oflow-loss regions separated by a portion of said substrate.
 10. Themethod recited in claim 7 wherein said substrate is comprised of ahigh-loss material.
 11. The method recited in claim 7 wherein saidcreating includes creating a low-loss region selected from a groupconsisting of: ABS plastic; air; ceramic; and Teflon.
 12. The methodrecited in claim 7 wherein said forming includes forming antenna traceslocated on opposing surfaces of said substrate interconnected by a viaextending through said substrate.
 13. A printed circuit board (PCB),comprising: a substrate having a footprint and a ground plane andconductive traces formed thereon, wherein said substrate has apredetermined radio frequency loss associated therewith; and an antennastructure, including: an antenna trace having a perimeter formed on aface of a substrate proximate a ground plane of said substrate and saidperimeter being substantially co-planar with said face, wherein saidsubstrate has a predetermined radio frequency loss associated therewith;and an low-loss region extending through said substrate and locatedbetween said antenna trace and said ground plane, wherein said low-lossregion is an opening located within said footprint that extendstransverse to and intersects said face, and wherein said low-loss regionhas a radio frequency loss less than said radio frequency lossassociated with said substrate, and wherein said low-loss region islocated outside said perimeter of said antenna trace.
 14. The PCBrecited in claim 13 wherein said substrate is comprised of a high-lossmaterial.
 15. The PCB recited in claim 13 wherein said low-loss regionincludes a plurality of low-loss regions separated by a portion of saidsubstrate.
 16. The PCB recited in claim 13 wherein said substrate has afootprint, and said low-loss region is an opening located within a saidfootprint of said substrate.
 17. The PCB recited in claim 16 whereinsaid low-loss region includes a low-loss material selected from a groupconsisting of: ABS plastic; air; ceramic; and Teflon.
 18. The PCBrecited in claim 13 wherein said antenna trace includes antenna traceslocated on opposing surfaces of said substrate interconnected by a viaextending through said substrate.
 19. An antenna structure, comprising:an antenna trace formed on a substrate proximate a ground plane of saidsubstrate, wherein said substrate has a footprint and a predeterminedradio frequency loss associated therewith; and a low-loss regionextending through said substrate and located between said antenna traceand said ground plane, wherein said low-loss region is an openinglocated within said footprint that extends transverse to and intersectsa plane of said face, and wherein said low-loss region has a radiofrequency loss less than said radio frequency loss associated with saidsubstrate, and said antenna trace does not overlap said low-loss region.